This invention relates to an electro-optical display device including the features of the invention.
Various types of electro-optical display devices and units are known, namely electro-optical display devices having liquid crystals or colloidal disperse systems as electro-optical material, electrochromic display devices and electrophoretic display devices. All of these display devices are passive display devices including the common feature that a cell is available which is limited by two parallel substrates. The substrates are held at a spacing of a few micrometers by a sealing material which may include spacing elements in such a way that a cell or a chamber is formed for the active electro-optical material. The first substrate in the direction of view is thereby always transparent and carries transparent electric conducting layers or electrodes whose shape corresponds to the signs or numerals to be indicated. The second substrate can either be transparent or not and also carries electrodes. The display device can be activated by applying a voltage to the electrodes. Such electro-optical display devices can indicate a plurality of conditions of an object to be measured, when the electrodes are subdivided in individual segments, which are for example controllable through an integrated circuit.
Semiconductive metal oxides, such as indium trioxide and tin(IV) oxide were successful in the practice. The preferred conducting layer material on the basis of indium trioxide is available under the trade name ITO. This material can be surfaced on a substrate by vaporising, vacuum sputtering or similar methods either in layers having the shape of the desired pattern of electrodes or as a single coherent layer in which the desired pattern of electrodes is provided thereafter by etching. Substrates surfaced with a thin coherent layer with a thickness of a few nanometers, for example glass plates coated with ITO, are available on the market.
The segments of the electrodes shaped in accordance with the desired pattern in addition to the sections positioned in the indicating area of the completed display device also include sections which lead to one of the borders of the substrate and via which the electric connection is effected. These areas are called metal conductors.
However the layer of electrodes cannot be directly provided with through-connections or bonded with metallic connecting leads normally made from copper or aluminium by usual physical methods of semi-conductor technology, such as soldering or ultrasonic welding, because the materials do not stick together. Moreover the layers have a relatively high electronic resistance, so that the metal conductors have to be supplied with voltages higher than desired in order to operate such a display device. Due to the high resistance the time constant of time delay after the expiration of which such a display device responds to an applied voltage, is also higher than desired. On these grounds it is necessary to provide the electrodes of the metal conductors with a metal coating.
On principle it would be possible to deposit a thin metal coating directly on a layer of semi-conductive metal oxides by means of metallising, vacuum sputtering or similar methods. When the metal is deposited in such a way the adhesion is effected by jamming the micro crystals mechanically. Due to the differing crystal lattices and lattice binding energies there is no diffusion or formation of mixed crystals between the metal coating and the layer of semiconductive metal oxides. This is why many metals stick to the layer only insufficiently, so that one is restricted in chosing the material or has to rely on depositing intermediate layers. As for instance the German specification OS No. 2,807,350 shows two chromium intermediate layers have to be deposited in order to be able to produce an adherent gold coating or an iron layer has to be deposited in order to be able to produce an adherent nickel coating. The intermediate layers and the coating are surfaced by vaporising or spraying. These methods require a high amount of energy and technology.
It is an object of the present invention to create an appropriate substrate for an electro-optical display device and that the electrode layer of this substrate, which layer includes one or more semi-conductive metal oxides, and the metal coatings used for electro-optical display devices directly adhere to this electrode layer. The substrate and thus the entire electro-optical display device is to be produced simply and economically.